The present invention relates to a novel L-glutamic acid-producing bacterium and a method for producing L-glutamic acid by fermentation using the same. L-Glutamic acid is an important amino acid as food, drugs and the like.
L-Glutamic acid has conventionally been produced by fermentation methods utilizing the so-called coryneform L-glutamic acid-producing bacteria which principally belong to the genera Brevibacterium, Corynebacterium, and Microbacterium or variants thereof (xe2x80x9cAmino Acid Fermentationxe2x80x9d, Gakkai Shuppan Center, pp. 195-215, 1986). As methods for producing L-glutamic acid by fermentation utilizing other bacterial strains, there have been known the methods utilizing microorganisms of the genera Bacillus, Streptomyces, Penicillium and the like (U.S. Pat. No. 3,220,929), the methods utilizing microorganisms of the genera Pseudomonas, Arthrobacter, Serratia, Candida and the like (U.S. Pat. No. 3,563,857), the methods utilizing variant strains of Escherichia coli (Japanese Patent Application Laid-Open (KOKAI) No. 5-244970(1993)) and the like.
Though the productivity of L-glutamic acid has considerably been improved by breeding of such microorganisms as mentioned above or improvements of production methods, it is still desired to develop a more inexpensive and more efficient method for producing L-glutamic acid in order to meet the expected markedly increasing future demand of the amino acid.
The object of the present invention is to find novel L-glutamic acid-producing bacterium having a high ability to produce L-glutamic acid, thereby developing a more inexpensive and more efficient method for producing L-glutamic acid.
To achieve the aforementioned object, the present inventors intensively searched for and studied microorganisms having the ability to produce L-glutamic acid that are different from the previously reported microorganisms. As a result, they found that certain strains derived from microorganisms belonging to the genus Klebsiella or the genus Erwinia had a high ability to produce L-glutamic acid, and have completed the present invention.
Thus the present invention provides:
(1) a microorganism belonging to the genus Klebsiella, the genus Erwinia or the genus Pantoea and having an ability to produce L-glutamic acid;
(2) a microorganism of the above (1) which is Klebsiella planticola or Pantoea agglomerans; 
(3) a microorganism of the above (1) or (2) which increases in an activity of an enzyme catalyzing a reaction for L-glutamic acid biosynthesis;
(4) a microorganism of the above (3) wherein the enzyme catalyzing the reaction for the L-glutamic acid biosynthesis is at least one selected from the group consisting of citrate synthase (abbreviated as xe2x80x9cCSxe2x80x9d hereinafter), phosphoenolpyruvate carboxylase (abbreviated as xe2x80x9cPEPCxe2x80x9d hereinafter), and glutamate dehydrogenase (abbreviated as xe2x80x9cGDHxe2x80x9d hereinafter);
(5) a microorganism of the above (4) wherein the enzyme catalyzing the reaction for the L-glutamic acid biosynthesis includes all of CS, PEPC, and GDH;
(6) a microorganism of any one of the above (1) to (5) which decreases in or is deficient in an activity of an enzyme catalyzing a reaction branching from a pathway for L-glutamic acid biosynthesis and producing a compound other than L-glutamic acid;
(7) a microorganism of the above (6) wherein the enzyme catalyzing the reaction branching from the pathway for L-glutamic acid biosynthesis and producing the compound other than L-glutamic acid is xcex1-ketoglutarate dehydrogenase (abbreviated as xe2x80x9cxcex1KGDHOxe2x80x9d hereinafter); and
(8) a method for producing L-glutamic acid which comprises culturing the microorganism as defined in any one of the above (1) to (7) in a liquid culture medium to produce and accumulate L-glutamic acid in the culture medium, and collecting the L-glutamic acid from the culture medium.
Because the microorganism of the present invention have a high ability to produce L-glutamic acid, it is considered to be possible to impart a further higher production ability to the microorganism by using the breeding techniques previously known for the coryneform L-glutamic acid-producing bacteria and the like, and it is expected to contribute to development of a more inexpensive and more efficient method for producing L-glutamic acid by appropriately selecting culture conditions and the like.